This invention relates to valve assemblies and valve stems, and in particular to valves the construction of which are optimized to reduce the sudden changes in pressure caused by routine mechanical opening and closing of the valves.
It is well known that the closing of a valve in the same direction as the flow of the fluid being controlled results in much more sudden and violent closure than closing of the valve against the flow. For this reason, conventional shut-off valves have been constructed and arranged this way for quite some time.
With respect to divert valves, though, with the normal arrangement where the inlet is in the center and the two outlets are disposed one above and one below the inlet, or one on each side, it has been conventional to close the valve in the same direction as the flow, as shown in Catalog No. AFC-90 published by Tri-Clover, Inc. The reason for this direction of closure for divert valves is that the two plugs, both affixed to the valve stem, prevent assembly of the valve if arranged any other way.
However, the sudden changes in pressure caused by closing valves in this manner can cause damage to a wide range of system components, ranging from pipe hangers to pumps and the clamps connecting the systems together. Alternatively, the avoidance of this hammering leads to otherwise unnecessarily low limits on the pressures, velocities and other capacities of the systems affected.
This invention relates to improvements to the apparatus described above and to solutions to some of the problems raised or not solved thereby.